Both in the case of self-ignition internal combustion engines and in the case of spark-ignition internal combustion engines, more and more vehicles are being equipped with a charging device, primarily in the form of exhaust gas turbochargers, in order to obtain greater engine power for the same engine size. With both types of internal combustion engine mentioned, the engine power attainable is limited, however, by the permissible degree of heating of the components, especially the permissible degree of heating of the material from which the exhaust manifold, the exhaust gas turbocharger and any necessary regulating valves and exhaust gas lines is made. To reduce the temperature of the exhaust gas it is customary in the case of spark-ignition internal combustion engines to run with an air ratio λ below the stoichiometric ratio. In some cases, the air ratio is in the order of magnitude of 0.7, which, however, in the upper load range of the internal combustion engine, results on the one hand in increased fuel consumption and on the other hand in increased CO emission. In view of the more stringent exhaust gas standards to be expected both in Europe and in the USA, increased CO emission is not acceptable.
Certain air-gap-insulated exhaust manifolds are conventional. These are normally used, however, to prevent cooling of the exhaust gas stream in the lower load range, that is, in the lower engine speed range, of an internal combustion engine whether it be a spark-ignition or a self-ignition internal combustion engine. This on the one hand has the effect that the efficiency of the exhaust gas turbocharger increases and on the other hand ensures that the catalytic converter enters the range of the optimum operating temperature as quickly as possible.